Programmatically adding a Curve bevel_object
After your edit I have a few more thoughts. You can't use a Mesh object such as produced by the primitive_circle_add() as a bevel_object, it needs to be a curve. Either make a wrapper function for bpy.ops.curve.primitive_bezier_curve_add, or include a small convert statement inside your vecCircle function (shown below).

In your loop the call to bpy.ops.object.convert doesn't complete and that's where you should start investigation, subsequent lines can be ignored until then.

Preconvert to Curve before a loop



Here's a massively simplified version of what you're doing. This is to get an understanding of how to bevel an object via a script. For simplicity I iterate over Curves here to emphasize where the problem is not! 

import bpy

def vecCircle(name, verts, obj_type='MESH'):
    bpy.ops.mesh.primitive_circle_add(vertices=verts)
    obj = bpy.context.active_object
    obj.name = name
    if obj_type == 'CURVE':
        bpy.ops.object.convert(target='CURVE', keep_original=False)
    return obj

tor0refCirc = vecCircle("tor0refCirc", 6, 'CURVE')

beziers = [o for o in bpy.data.objects if o.type == 'CURVE']

for circleObj in beziers:
    circleName = circleObj.name
    circleObj.data.bevel_object = tor0refCirc


turns this:
  

into this:
  

Convert to Curve during the loop



But if your original objects are meshes, they do need to be converted either on-mass before the loop, or during the loop.

import bpy

def vecCircle(name, verts, obj_type='MESH'):
    bpy.ops.mesh.primitive_circle_add(vertices=verts)
    obj = bpy.context.active_object
    obj.name = name
    if obj_type == 'CURVE':
        bpy.ops.object.convert(target='CURVE', keep_original=False)
    return obj

tor0refCirc = vecCircle("tor0refCirc", 6, 'CURVE')

# ensure no selected objects
bpy.ops.object.select_all(action='DESELECT')

pre_beziers = [o for o in bpy.data.objects if not (o.name == 'tor0refCirc')]

for circleObj in pre_beziers:
    circleName = circleObj.name
    circleObj.select = True
    bpy.context.scene.objects.active = circleObj   # &lt;&lt; -- important
    bpy.ops.object.mode_set(mode='OBJECT', toggle=False)
    bpy.ops.object.convert(target='CURVE', keep_original=False)    
    circleObj.data.bevel_object = tor0refCirc
    circleObj.select = False    


which turns Mesh into Curve before adding bevel_object:  

  

like this  ( you might want to increase resolution 6 vertices may be too coarse)